Amazon has been on the Federal Aviation Administration’s naughty list for a few years, with at least 24 violations for shipping hazardous materials. But now the agency is proposing a $350,000 fine after Amazon sent, via air, a package labeled “Amazing! LIQUID FIRE” from Louisville, Ky., to Boulder, Colo., on Oct. 15, 2014, Reuters reports.

That “amazing” drain cleaner injured nine UPS workers when the package leaked, and the workers had to be doused with chemical wash after experiencing a burning sensation.

The FAA contends the package wasn’t packaged or labeled correctly, considering its corrosive contents, and didn’t come with the form required for shipping dangerous goods. Per USA Today, the 1-gallon container was labeled with a skull and crossbones, as well as the warnings “causes severe burns” and “corrosive to eyes and skin,” but that container was packed inside a fiberboard box.

The Wall Street Journal notes that the proposed fine comes right as Amazon is diving deeper into the shipping arena with its own fleet of planes and trucks—and also as the FAA is getting tough on those who flout its rules on hazardous materials.

The agency says that between February 2013 and September 2015, Amazon was hit with the two dozen regulation violations—resulting in at least 15 packages that leaked and totaling nearly $1.3 million in fines, per Reuters—and notes that it’s going to keep a close eye on the retailer’s shipping protocol.

“We take the safety of our air cargo delivery partners seriously,” an Amazon rep says, promising to keep working with the FAA. Gizmodo, for its part, says Amazon “should have known better,” based on reviews of the product alone—one of which says it’s “mutually assured destruction in a bottle.”